1. Field of the Invention
This invention relates to an improved film-wrapped blasting cartridge, particularly a chub cartridge containing a water-bearing blasting agent.
2. Description of the Prior Art
Semi-solid colloidal dispersions of water-bearing blasting agents, e.g., water gels or slurry explosives, or emulsion-type blasting agents, currently are available in the form of film-wrapped cartridges, often referred to as "chub" cartridges. The chub cartridge is a tube of plastic film, filled with blasting agent, and gathered at both ends and closed, e.g., by means of metal closure bands around the gathered portions.
Chub cartridges of water-bearing blasting agents which are used to initiate the detonation of adjacent non-cap-sensitive blasting agents in boreholes, e.g., adjacent chub cartridges or a detonable mixture of ammonium nitrate and fuel oil (ANFO), are known as primer cartridges, which are "primed" in the field by various techniques to form primer assemblies. Priming involves affixing to the chub cartridge an initiating means such as a detonating cord, an electric blasting cap, or an nonelectric blasting cap and detonating cord, any of which may, if necessary or desirable, be positioned in initiating relationship with the cartridged blasting agent via a small tubular booster to form the primer assembly.
According to present practice, for example, a chub cartridge of a cap-sensitive blasting agent can be primed by punching a hole in the side or end of the cartridge, inserting an electric blasting cap into the blasting agent, and tying one or two half-hitches, depending on cartridge diameter, around the cartridge with the cap leg wires to support the cartridge weight during loading and to hold the cap in position. A chub cartridge of cap-sensitive blasting agent can also be primed by a 4.5 gram/meter or larger detonating cord placed inside, or along the outside of, the cartridge. This is presently accomplished by punching holes in opposite sides of the cartridge, threading the cord through the cartridge, and knotting the cord outside the cartridge; or by taping the cord along the outside of the cartridge.
For use with non-cap-sensitive blasting agents, the blasting cap or detonating cord that is to initiate the detonation of the blasting agent in the chub cartridge is supplemented by a small cap-sensitive booster, e.g., a mixture of pentaerythritol tetra-nitrate and an elastomeric binder extruded in the form of a tube, which is placed around the blasting cap or detonating cord before insertion into the blasting agent.
The described techniques of priming chub cartridges of blasting agents suffer from certain drawbacks. First, with certain blasing compositions and packaging films, the punching of one or more holes in the film introduces the possibility that the composition might to some extent become desensitized by water in wet boreholes. Naturally, it would be advantageous to eliminate the need to punch holes in the cartridge where possible, especially if the package film is one which readily propagates a tear, or if the blasting composition is subject to desensitization by water. Secondly, the tying of half hitches around cartridges is time-consuming and bothersome. Thirdly, the taping of cord to the cartridges also is time-consuming and, more importantly, could lead to failure if the taping should fail to provide the necessary intimate contact between the cord and cartridge along substantially the entire length of the cartridge.
In some methods of blasting, explosive cartridges are loaded in a borehole in a manner such that there is a spacing between their ends filled with an inert material (e.g., as in smooth blasting or trenching), or with a less-sensitive blasting agent that is to be detonated by the detonation of the spaced cartridges (e.g., to initiate ANFO compositions). In certain situations in which it is desired to position the cartridges end-to-end, such positioning can be destroyed by the collapse of the borehole. In all such cases in which the propagation of a detonation between cartridges cannot be assured, each cartridge has to be primed, and with chub cartridges this has usually been done by taping each cartridge onto a common detonating-cord downline. This procedure is time-consuming and, as mentioned previously, can fail to provide the required contact between cord and cartridge.
Rigid explosive containers such as metal or plastic cans have heretofore been adapted to have detonating cord held in place along their periphery by the application of a sleeve or cartridge coupler to the container. For example, U.S. Pat. No. 3,332,349 describes a rigid, continuous explosive column of cartridges joined end-to-end by couplers with a detonating cord threaded between the walls of the cartridge and surrounding couplers. U.S. Pat. No. 3,789,760 describes a primer can and a sleeve fitting around the can and cooperating therewith to form recesses adapted to receive a blasting cap or detonating cord for actuating the primer. Similar container/sleeve combinations are described in U.S. Pat. Nos. 4,023,494 and 4,037,536.
U.S. Pat. No. 1,512,714 describes a stick of explosive having a heavy paper wrapper or casing wherein a longitudinal passage or channel is formed for retaining safety fuse adjacent the side of the stick, the walls of the channel being of double thickness and strong enough to hold their shape during shipment and handling. One end of the fuse is connected to a blasting cap which fits into an axial hole in the stick, and the channel holds the fuse and cap against displacement by a direct longitudinal pull. The paper wrapper has flaps which fold down over the ends of the stick and have to be opened up temporarily to allow attachment of the cap and fuse.